The present invention relates to a blind rivet assembly with localized attachment and methods of assembling, and particularly to a multiple part blind rivet assembly with localized attachment points, and further relates to a method of assembling multiple parts of a blind rivet assembly.
Blind rivets normally comprise two parts, a mandrel and a body. The mandrel and body are assembled together, and inserted into a hole in a workpiece from the operator""s side. By applying a suitable setting tool, the mandrel is pulled and, by pulling the mandrel the rivet body is upset on the side remote from the operator, thus securing the joint. For pull system blind rivets during the process of setting the rivet the mandrel head enters the rivet body and expands the rivet body by virtue of the mandrel head distending the outer diameter. The mandrel continues to be progressively pulled through the rivet body until it meets resistance on the blind side of the workpiece at which point the mandrel ruptures at a predetermined break load. Although the mandrel is held in the rivet body before setting, once set the retained part of the mandrel can be removed, using varying degrees of force depending upon the design of the rivet. Moreover, it is sometimes the case that, after setting, the mandrel part is free to move within the rivet body without needing force to dislodge it from its setting position. The end users of rivets need to be confident that the mandrel will remain in the rivet body, and will not move to cause noise problems or fall into the assembled workpiece.
It is an object of the present invention to provide a blind rivet in which the above disadvantages are reduced or substantially obviated, which rivet additionally demonstrates improved setting characteristics. It is a further object of the present invention to provide an improved method of assembling a blind rivet.
The present invention provides a blind rivet assembly which comprises a mandrel and a rivet body, the mandrel comprising a head portion and a shank portion and the rivet body comprising a generally cylindrical body portion terminating in a flange at a first end thereof and a free end at the other end thereof, the mandrel being assembled into the rivet body so that the free end of the body portion of the rivet body contacts the underside of the head portion of the mandrel characterized in that the free end of the body portion of the rivet body is attached to the underside of the head portion of the mandrel.
In one realization of the present invention, the free end of the body is friction welded to the underside of the head portion of the mandrel.
One of the benefits of using friction welding is that the process facilitates the joining of materials that are difficult to weld resulting in a rivet body and mandrel joined without further finishing necessary.
One beneficial aspect of the rivet according to the present invention which is formed by friction welding is that the rivet body and the mandrel each have features formed on the outer surfaces to facilitate rotation in a special machine. The rivet body and the mandrel can be easily rotated in opposite directions.
With the friction welding process there is generated displaced material from the interface of the rivet body and the mandrel. It is desirable to keep this displaced material within the profile of the rivet envelope and therefore ideally a space is provided to accommodate this excess material.
The present invention further provides a first method of assembling a rivet assembly, wherein, before assembly, the mandrel has, beneath its head portion, one or more projections, and the method of assembling the rivet assembly includes the steps of discharging an electrical current between the rivet body and the projections on the mandrel, causing both the free end of the rivet body, and the projections to melt, switching off the current, and pressing the head portion of the mandrel towards the free end of the rivet body.
During the setting process the rivet is applied in the normal manner but, since the mandrel head is attached to the end of the rivet body, the mandrel head does not enter the rivet body as the mandrel is pulled. The setting characteristics of the rivet change in that the rivet body is subjected to a compressive load and the rivet body expands radially outwards on the blind side of the workpiece; the resulting bulge being greater in diameter than if the mandrel head were pulled into the rivet body. Thus the set rivet will have greater tensile strength.
The present invention further provides a second method of assembling a rivet assembly according to the present invention where the free end of the body portion of rivet body is friction welded to the underside of the head portion comprising the steps of locating the mandrel within the rivet body so that the bottom section locates with the recess and at least part of the wall of the recess is in contact with part of the surface of the bottom section, rotating the mandrel in relation to the rivet body to generate heat due to friction between the wall of the recess and the surface of the bottom section and, when the interface material is molten, pressing the head portion of the mandrel towards the free end of the rivet body whilst holding the mandrel and rivet body stationary until the interface material cools.
Other objects, features and advantages of the present invention will become more fully apparent from the following detailed description of the preferred embodiment, the appended claims and the accompanying drawings.